Hollow shaft gearbox choice: worm gear or bevel gear?

What is the right hollow shaft gearbox for me? This is a frequently asked question by (new) customers of Apex Dynamics. To come to a good choice there are then two important questions to answer. In practice, people often make a choice between a bevel gearbox and a worm gearbox. (We leave the hypoid variant aside for the moment.) We also discuss these considerations in this article so that you can come to a clear choice yourself.

Choose hollow shaft gearbox

Apex Dynamics often receives the question "We want a gearbox with hollow shaft, which one should I choose? In itself this is a logical question, but to come to a good choice we need more data. In fact, only 2 questions are needed to determine the right series(s). In determining the type of hollow shaft, there are 2 criteria:

• Should the hollow shaft be continuous or not?
• Should the hollow shaft be form or force locked?

Continuous hollow shaft

In fact, a hollow shaft does not have to be continuous, it can also end in a shaft stub with a clamping ring. If you want it continuous, the output stage of the gearbox is always perpendicular. As can be seen from the table below, based on this choice, already half fall off.

Hollow shaft form- or force-locked

The characteristic of a joint based on a force closure is that if the force pressing the parts to be joined is lost, the joint is no longer secured. In other words, by clamping, pressing or crimping, the parts are joined together. This transmission is always backlash-free. A well-known example is the handbrake of a car or a wedge under a door.

The opposite of force-locked is shape-locked. The force is then transmitted by the shape of the floating and driven object. Well-known examples of this include rivets and keyways. Especially with keyways, there can be a tad of play.

Other considerations

What is next interesting : How much clearance is allowed and is the hollow shaft used for the passage of cables and the like?

Hollow shaft gearboxes overview

In the table below an outline of the possibilities within the program of Apex Dynamics :

Worm gear and bevel gear comparison

Apex Dynamics has no worm gearboxes in its program. The low efficiency in combination with the relatively expensive (servo) drive is in our opinion not an optimal combination. In practice it is even often a bit strange. After all, you generally choose a servo motor for accurate positioning, otherwise you could just take a three-phase motor with encoder feedback. At the same time, we see that you often have to take a more powerful (thus more expensive) servo motor and driver to compensate for the poor efficiency. In other words, the combination of a servo motor and a worm gearbox is illogical. It is often more interesting to choose a bevel gearbox.

Key considerations for choosing a worm or bevel gearbox:

• Friction and wear - The gears in a bevel gear roll over each other, this reduces friction and thus increases efficiency. The gears in a worm gear slide over each other, causing friction and wear.
• Purchase price - In many cases, a worm gearbox is cheaper to produce and thus usually has a lower purchase price than a bevel gearbox.
• A worm gear can have a degree of self-braking. However, this is not allowed for CE directive, which requires a separate mechanical brake.
• Accuracy, a bevel gearbox has a low, permanent backlash. Of a worm gearbox, the backlash increases freely due to friction and in some cases is adjustable.
• Efficiency - The efficiency of a worm gearbox at a large gear ratio is about 50%, a bevel gearbox in a similar situation has an efficiency of >90%.

Which hollow shaft gearbox best suits your application? We are happy to help you make this choice. We share our knowledge and experience with similar applications so you know exactly what impact this choice will have on the rest of your application or, for example, maintenance and efficiency.

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